I dont know why your new computers are going in the Domain Admins OU, however http://support.microsoft.com/kb/324949/ explains how you can change the default OU for new objects and may cure your problem.

This tutorial will walk an individual through the process of transferring the five major, necessary Active Directory Roles, commonly referred to as the FSMO roles from a Windows Server 2008 domain controller to a Windows Server 2012 domain controlle…

Sometimes it takes a new vantage point, apart from our everyday security practices, to truly see our Active Directory (AD) vulnerabilities. We get used to implementing the same techniques and checking the same areas for a breach. This pattern can re…